In the biblical account of Noah's Ark, pitch was used to seal the vessel against water.
Genesis instructs Noah to cover the ark with pitch inside and outside. The coating would make the wooden structure watertight, just as bitumen-like substances were used in ancient boatbuilding and construction. The biblical wording presents sealing as a practical part of preparing the vessel.
Pitch is a broad term for a sticky waterproofing substance, and translations vary in the precise wording used for the material. Some versions use “bitumen” or related terms, reflecting differences in how ancient languages and substances are understood.
The instruction to coat both the interior and exterior is distinct from the type of wood used to build the ark. It also differs from later artistic depictions, which often focus on the ark's shape while omitting the engineering detail. The text gives no modern chemical formula for the coating.